Ultraviolet Raman Wide-Field Hyperspectral Imaging Spectrometer for Standoff Trace Explosive Detection.

We constructed the first deep ultraviolet (UV) Raman standoff wide-field imaging spectrometer. Our novel deep UV imaging spectrometer utilizes a photonic crystal to select Raman spectral regions for detection. The photonic crystal is composed of highly charged, monodisperse 35.5 ± 2.9 nm silica nanoparticles that self-assemble in solution to produce a face centered cubic crystalline colloidal array that Bragg diffracts a narrow ∼1.0 nm full width at half-maximum (FWHM) UV spectral region. We utilize this photonic crystal to select and image two different spectral regions containing resonance Raman bands of pentaerythritol tetranitrate (PETN) and NH4NO3 (AN). These two deep UV Raman spectral regions diffracted were selected by angle tuning the photonic crystal. We utilized this imaging spectrometer to measure 229 nm excited UV Raman images containing ∼10-1000 µg/cm2 samples of solid PETN and AN on aluminum surfaces at 2.3 m standoff distances. We estimate detection limits of ∼1 µg/cm2 for PETN and AN films under these experimental conditions.

Raman hyperspectral imaging spectrometer utilizing crystalline colloidal array photonic crystal diffraction.

We fabricated a novel hyperspectral Raman imaging spectrometer that, for the first time, uses a photonic-crystal wavelength-selecting device to select a narrow-wavelength spectral interval. The photonic crystal consists of an array of highly charged, monodisperse polystyrene particles that self-assemble into a face-centered cubic crystal. The photonic crystal Bragg-diffracts a narrow spectral interval that can be tuned by altering the incident angle of collimated Raman scattered light. Our prototype spectrometer diffracts a ~200 cm(-1) interval of the 488 nm excited visible Raman spectrum of Teflon. This enabled us to select a close-lying triplet of Teflon Raman bands. We imaged the Teflon surface by focusing this narrow region onto a charge-coupled device to create a Raman image of the sample surface that spectrally details the chemical composition.

Ruthenium dihydroxybipyridine complexes are tumor activated prodrugs due to low pH and blue light induced ligand release.

Ruthenium drugs are potent anti-cancer agents, but inducing drug selectivity and enhancing their modest activity remain challenging. Slow Ru ligand loss limits the formation of free sites and subsequent binding to DNA base pairs. Herein, we designed a ligand that rapidly dissociates upon irradiation at low pH. Activation at low pH can lead to cancer selectivity, since many cancer cells have higher metabolism (and thus lower pH) than non-cancerous cells. We have used the pH sensitive ligand, 6,6'-dihydroxy-2,2'-bipyridine (66'bpy(OH)2), to generate [Ru(bpy)2(66'(bpy(OH)2)](2+), which contains two acidic hydroxyl groups with pKa1=5.26 and pKa2=7.27. Irradiation when protonated leads to photo-dissociation of the 66'bpy(OH)2 ligand. An in-depth study of the structural and electronic properties of the complex was carried out using X-ray crystallography, electrochemistry, UV/visible spectroscopy, and computational techniques. Notably, RuN bond lengths in the 66'bpy(OH)2 complex are longer (by ~0.3Å) than in polypyridyl complexes that lack 6 and 6' substitution. Thus, the longer bond length predisposes the complex for photo-dissociation and leads to the anti-cancer activity. When the complex is deprotonated, the 66'bpy(O(-))2 ligand molecular orbitals mix heavily with the ruthenium orbitals, making new mixed metal-ligand orbitals that lead to a higher bond order. We investigated the anti-cancer activities of [Ru(bpy)2(66'(bpy(OH)2)](2+), [Ru(bpy)2(44'(bpy(OH)2)](2+), and [Ru(bpy)3](2+) (44'(bpy(OH)2=4,4'-dihydroxy-2,2'-bipyridine) in HeLa cells, which have a relatively low pH. It is found that [Ru(bpy)2(66'(bpy(OH)2)](2+) is more cytotoxic than the other ruthenium complexes studied. Thus, we have identified a pH sensitive ruthenium scaffold that can be exploited for photo-induced anti-cancer activity.